82 Inside the Living Cell 



while there, in the spring of 1923, he heard of the discovery of 

 insuUn and at once went to obtain the treatment. He soon recovered 

 and has been able to lead a normal and productive life during the 

 last 26 years. 



As we have seen (Fig. 3), insulin is a very complex substance and 

 has not yet been synthesized, and until this has been achieved dia- 

 betics will remain dependent on the supplies of insulin which can be 

 obtained from animals. 



Above the kidneys are two small glands, known as the suprarenals. 

 Each suprarenal consists of two distinct glands, as their inner parts 

 have quite a different function from the outer layers. It was found 

 in 1895 by Oliver and Schafer that extracts of the inner part pro- 

 duced very marked physiological actions, and some years afterwards 

 an active substance called adrenaline was isolated from them. In due 

 course the structure of adrenaline was found; it has been synthesized, 

 and the synthetic product has exactly the same action as the natural 

 substance. It is also quite a simple substance. Introduced into the 

 blood-stream, it causes an increase in the blood-pressure, a quicken- 

 ing of the heart-beat, and an increase of blood sugar. It tones up the 

 body and makes it ready to meet unusual stresses. The gland is 

 stimulated by the sympathetic nervous system. Strong mental 

 stresses such as fear, anger, and strong emotion, all cause it to 

 secrete adrenaline into the bloodstream. The result is to stimulate the 

 heart and prepare the body to meet unusual demands upon it. The 

 gland thus acts as a kind of relay station — an intermediary between 

 the brain and the chemical regulating mechanisms. The tiny nervous 

 impulses from the brain enter the gland and cause it to release the 

 hormone, which is carried by the blood to all parts of the body. This 

 is naturally a relatively slow process, and when adrenaline has been 

 released its effects only wear off slowly, so that when you have had a 

 fright your heart continues to palpitate for some time after the cause 

 has disappeared. 



The outer layers of this gland produces quite different substances. 

 It was not until 1931 that Swingle and Pfiffner succeeded in preparing 

 stable extracts of the cortical hormones which would maintain life in 

 an animal deprived of the gland. Soon after that, crystalline sub- 

 stances were obtained in several laboratories and their chemical 

 nature was worked out. They belong to a group of substances called 

 steroids which have the same rather unusual hydrocarbon nucleus, 

 which is the central structural feature of a number of apparently 

 unrelated compounds (see Appendix, Fig. 7, III). It turns up in the 

 bile-acids, in vitamin D, and in the sex hormones which are mentioned 

 below. 



